Vibration at 16-17 km/h

[tympos]

I have around 500km with my Cube Nature one. I really like the bike, couldn't be more happy.
However, at around 250-300km I started feeling a vibration at speed of around 16-17km/h coming from the back of the bike (maybe). The vibration wasn't there at the beginning, I am pretty sure about this. The only thing that changed is the addition of a Cube rack. However, even with the rack the vibration wasn't there, at least for the first days.
I can feel it at the seat and at the pedals. It is not very intense, but it's there.
It happenns with the motor on or off, pedaling or no pedaling, so I hope it is not related to the motor.
Other people with more weight than me do not feel it, as they say!!!
I also noticed that when I feel it and I am in an open area if I turn i.e. have some tilt (angle between the bike axis and the horizon) it seems to go away. I dont know if it has to do with speed reduction, tire contact point or anything else.
I took it to the shop, where the vibration was confirmed by the shop owner who has the same weight as me more or less. He said it's probably something related to the tire, he took the wheel out and checked some screws that were ok.
Any suggestion on what could be, how to find what is causing the problem or anything else that would help would be much appreciated!!!

 

[AHicks]

Tire tread pattern? Thinking knobby vs. slick. The knobby will nearly always run with a slight vibration and hum. Slick will be quiet and smooth/no vibration.

 

[tympos]

Thank you AHicks, but wouldn't this be felt all the time if it was just the tread pattern? There is no vibration at other speed except at 16-17km/h.
The tires are the Schwalbe Land Cruiser, Active, 55-622
They can be seen here.
Obviously I am not goint to change tires now just for this reason, except if I find some suggested tires, much better than these, at a reasonable price. I mostly use the bike at city roads so I suppose I could use "slickier" tires.
I also have not cleaned/lubricated the chain yet, so this could be another reason as I read in other forum posts.
Question: In general, after how many kms do we change tires and clean/lubricate the chain?

 

[Brockrock]

Is it possible that your tires have dropped in air pressure over this time? That could explain the change. Bike tires do very slowly leak down over time, and a puncture is not required. I clean my chain with 3 in 1 oil every other ride which is about every 60 miles. I squirt the oil on a clean cloth and spin the chain while wiping it down.

 

[AHicks]

Those tires should be fine as long as they are inflated properly - to the point those "knobs" on either side of the center tread are not making contact with the hard/paved surface.

Tires differ greatly due to tread design. Some start out nice and smooth, only to get noisey as the speed increases.

Second the fact that tires leak down regularly - until you put something like Slime in them. That seals the microfine holes that allow any tube I've ever had to leak air.

 

[Mike TowpathTraveler]

My scenario regards to a sudden rear end vibration is likely going to be waaaaay out in left field, but it might be worth considering..... In early April, 2018, I was moving along at about 19 mph on asphalt road shoulders onboard my Haibike Full FatSix. The location was urban South Broad Street, Trenton, NJ. As I was booking along, a UPS truck decided he was going to enter South Broad Street at the moment I was about 25-30 feet in front of him, making eye contact with me.

I had to jam on the breaks, skidding the rear tire at 19 mph. And right after, a severe vibe like my tire was out of balance, for the rest of the 10 plus miles until I got home.

This is what my rear tire looked like. Note the mold casting located dead centerline of the tubed tire, a Schwalbe Jumbo Jim 26 x 4.0...... note the dark rubber around the tread blocks in the area of the deranged center of the tire, this was where I skidded the tire on that roadside shoulder asphalt.

The bead stayed locked, however, at near 30 psi tire pressure, it looks like the outer tire casing "walked" or moved. Though I bought a new tire to replace this one, I found by breaking the bead, separating the rim and tire and remounting it, the deranged area of the casing relaxed itself into proper alignment with that mold casing line straightening itself out. Hard to believe and really out there as to possibly being your problem, but it's worth a mention. Also: recheck your motor mount bolt torque with a torque wrench as well as spinning the tire on the bike and just observing the spin for any abnormality.....

In both pics, note how the right side outer edge of the tire in the area of the centerline and tread derangement; how crooked the tire casing appears....

 

[tympos]

What is the acceptable difference in radius for a tire? I rotated the tire and noticed that there is a spot, more like a small area, an arc of the tire, that has slightly larger radius than the rest. The difference in the radius is about half a centimeter (that's about 1/5 of an an inch). So the tire is not a perfect circle. Could this be the cause of vibrations?

 

[AHicks]

I had something like that happen to a tire on my bike a while back. I wasn't watching where I was going and drove through a big pot hole - damaging the tire. I'm thinking I noticed that at low speeds though?

How about swapping your front tire to the rear for a try - to see if the vibration changes?